Rear speakers on 04 dodge caravan with DVD

Need some help please. Just replace our worn out 92 Voyager with a (new to us) 2004 Dodge Grand Caravan that came with factory DVD palyer. The instruction sheet say to press the "mode" button on the
remote to select "rear speakers off" so the kids can watch there movie (using headphone) and we can still listen to the the radio or CD up front.
Problem is when I press the mode button nothing happens, no displays and rear speakers do not turn off. I can not find any button on either the radio, 6 disc changer or the screen to do this either.
Only way I can do this is to use the fader control on the radio to fade out the rear speakers.
Am I missing something? Headphones work but no "back speakers off" function as the instructions state. Is this feature broken or are the insteructions universal and I don't have this feature.
My set up which appears all factory;
in dash am/fm cassette CD palyer, 6 disc cd/dvd in dash player
TIA
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check battries in remote or could be wrong remote

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Their should also be a button by the radio with a picture of headphones (I think) that when you press it will turn off the rear speakers.
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